This invention relates to dual lumen cannulae for medical use, and more particularly for semipermanent means for simultaneously withdrawing blood from the subclavian vein for extra corporeal processing and returning the treated blood back to that vein at the same site.
Dual lumen cannulae have been proposed and used for hemodialysis because they provide the advantage of simultaneously withdrawing and returning blood of a patient through a single puncture rather than two. Such cannulae have been made of rigid metal tubes and are in general of two types: those with concentric flow lumens such as disclosed in U.S. Pat. No. 4,037,599 and those with parallel channels as in U.S. Pat. No. 4,203,436. These types are only suitable for a single blood treatment and must be emplaced in and removed from the patient for each use. None of them is flexible or suitable for emplacement in the subclavian vein. While these cannulas have proven useful, there would be an advantage for a cannula that can be left in place for several uses.
Single lumen cannulae suitable for semipermanent placement in the subclavian vein are known. These can be left in place for one to two weeks. One such type is the "Vas-Cath" subclavian cannula sold in the United States by Shiley Incorporated. These devices perform satisfactorily, but they require a more complex hemodialysis apparatus that must sequentially take in blood, treat it, return the treated blood to the patient. These steps cannot be done simultaneously as is most desirable.